There are two forms of yellowing teeth, one is dentin yellowing, which is yellowing from the inside out. You can use cold light whitening technology to whiten your teeth, but it can only raise about two shades at a time, and if you are not satisfied with the color, you can continue whitening at intervals, and the whitening effect can only last about three years. Veneers and porcelain crowns are very harmful to the teeth and require the removal of the hardest enamel layer on the surface of the teeth, which may lead to pulpitis later. The other is yellow from the outside to the inside, if it is yellow from the outside to the inside, it may be a tooth stain on the surface of the tooth, which can be directly removed by conventional scaling and polishing.